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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"


remainder being water. The crude acid, also found on the market, is yellow-
ish or brown and contains 20-50% of the acid. The ordinary impurities
are various mineral acids and salts, organic acids (acetic, butyric, tartaric,
citric), sugars, glycerine, mannitol.

1.  Extraneous Acids.—The acid diluted in the proportion i : 10 and
acidified with nitric acid, should give no turbidity with barium nitrate
(sulphuric acid or sulphate) or with silver nitrate (hydrochloric acid or chloride).

i part of the acid is diluted with 5 parts of 96% alcohol and filtered,
the filtrate being treated with a little hydrochloric acid and a few c.c. of
10% calcium chloride solution and boiled: the presence of free sulphuric
acid is indicated by a turbidity appearing either immediately or after a
short time.

When distilled with steam, the acid should give a distillate which is
not rendered turbid by silver nitrate (free hydrochloric acid).

i c.c. of the acid, neutralised with about 60 c.c. of lime water, should
not become turbid either in the cold (oxalic, tartaric or phosphoric acid) or
in the hot (citric acid).

i c.c., gently heated, should not evolve an odour of fatty acids (acetic,
butyric acids).

2.  Mineral Salts.—The acid diluted in the proportion i: 10 should
not change with hydrogen sulphide, or ammonia and ammonium sulphide
or oxalate, or potassium ferrocyanide (copper, lead, zinc, calcium, iron).

10 c.c., carefully calcined, should leave no appreciable residue.

3.  Various Impurities.—i c.c., poured by drops into 2 c.c. of ether,
should dissolve to a clear liquid (absence of sugars, mannitol, gum, calcium
phosphate, etc.).

i c.c., neutralised with magnesium oxide, evaporated to dryness on
a steam bath, and the residue taken up in absolute alcohol, filtered and
evaporated, should leave no sweet, syrupy residue (glycerine),

I c.c., mixed carefully (avoiding rise of temperature) with i c.c. of
cone, sulphuric acid, should not produce a brown coloration (sugars).

4.  Quantitative Determination.—In absence of other acids, the lactic
acicl may be estimated by means of a standard alkali:  to 10 c.c. (or 10
grams) are added 20 c.c. of N-sodium hydroxide and a few drops of phenol-
phthalein and the liquid boiled for 10 minutes and the excess of alkali
titrated with normal hydrochloric acid :   i c.c.  N-NaOH = 0-09 gram

With crude, impure products, the lactic acid is estimated by Ulzer and
Seidel's method,1 which consists in oxidising by means of alkaline potassium
permanganate and then determining the oxalic acid formed. The presence
of oxalic acid or of glycerine must, of course, be excluded.


HN03 = 63

This is found in commerce as crude or commercial acid, usually yellowish,
D = 1-33-1-40, containing 52-65% HN03; as pure acid, which is colourless

1 Chem. Zeit., 1897, p. 204.er or, better, of paraffin. It may be contaminated